The world's energy demand is increasing, and the fossil fuel sources are depleted, leading to increasing competition for the available energy sources, and thereby hampering economic growth by high energy prices. To overcome this situation, renewable energy sources must be brought into exploitation. With the present-day technology, the only renewable energy source which has sufficient capacity to cover significant parts of the energy demand is biomass conversion. Biomass is efficiently converted into heating and electricity by existing technologies, but transportation fuels, which accounts for one third of the total energy consumption, must be available as high energy density fluids, preferably compatible with fossil fuels like diesel oil and gasoline. Therefore technologies for transforming and intensifying the energy content of biomass are required.
Methods for producing bio-ethanol are known. It typically involves a number of unit operations such as feedstock preparation, fermentation and by-product purification. Each of these unit operations may comprise several unit operations. Such prior art method have a number of draw backs. Firstly, bio-ethanol is mainly produced from starch and sugar rich biomass such as corn and wheat grain. Already in the feedstock harvesting step ½ to ⅔ of the plant material is often rejected, and mainly the seeds are used in the fermentation. Various methods are being developed to increase the amount of plant material which can be converted in the conversion step. Such methods include enzymatic hydrolysis of the starch to produce glucose which can be converted in the fermentation. Typically the entire feed stock is processed i.e. the feed pulp also includes the cellulostic parts and other materials, which are not converted in the fermentation. Hence, prior art methods include up-grading the residual material from the fermentation to a dry material after separation from the ethanol produced. This upgraded material may be used as cattle feed. The market for the upgraded by-product is not expected to match the production, if a large number of bio-ethanol plants are put into operation. It is therefore desirable to find an alternative use of the by-product. Secondly many of the unit operations involved in prior art method have a relative high energy consumption thereby increasing the production cost of the bio-ethanol. Thirdly a large amount of the plant installation cost is related to up-grading of the residual material e.g. decanting and drying, and especially the drying is very energy consuming. Furthermore, existing methods for producing bio-ethanol is limited to specific feed stock. It is highly desirable to enable conversion of other materials such as waste materials eventually in to other types of products, such as oils.